It's a measure of AMD's spunk that the Santa Clara CPU company first unveiled plans for the Athlon XP during the Intel Developer's Forum in August. About the only thing they could have done that was more cheeky was to take a booth at IDF and give demos.

The Athlon XP builds on the Athlon core by adding a few new features and tweaking the chip design a bit to run cooler. The result is a CPU that runs at 1.53GHz using a very stock Coolermaster all-aluminum (no copper) cooler. We've written extensively about the Athlon microarchitecture before, so we'll just touch on the new features:

3DNow! Professional adds 52 new instructions to the Athlon's SIMD (single-instruction, multiple data) instruction set. This is essentially the entire SSE instruction set, which is new to AMD, but has existed in Intel CPU's since the Pentium III. The addition of SSE will enable AMD to compete with Intel on a performance basis with some media encoding and decoding applications. AMD is still playing catch-up, though, as Intel's newer SSE2 instructions offer 64-bit wide, double-precision SIMD FP capability, and can process two 64-bit Integer MMX operations concurrently.

Hardware Data Prefetch lets the Athlon XP pull data into the L2 cache before it's needed. New logic has been added to better judge when to prefetch data. This effectively reduces cache latency and increases effective memory bandwidth.

A new thermal diode reduces the likelihood of catastrophic failure if a cooling fan fails.

These new features only add a half-million transistors, boosting the transistor count to 37.5 million from 37 million. At the same time, tweaks to the die layout have resulted in 20% less power consumption. Like the previous Thunderbird, the Athlon XP has 384KB of total cache (128KB L1 and 256KB L2).

The Athlon XP comes in a newer packaging style, known as "organic pin grid array". The substrate material is fiberglass, similar to that used in printed circuit boards. This lowers both cost and impedance within the package.